“We must end the hypocrisy of senior politicians admitting to using cannabis in younger years – and describing it as ‘youthful indiscretions’ – whilst condemning tens of thousands of their less fortunate fellow countrymen and women to criminal records for precisely the same thing, blighting their careers.”

A briefing ahead of the debate this afternoon by Transform said four US states – Alaska, Colorado, Oregon and Washington – and the capital, Washington DC, have legalised cannabis for non-medical adult use.

It claims legalisation in Colorado, where retail shops opened for the first time last year, has not led to an increase in pot use among young people.

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MODEL: UK should look at the recent successes of legalising cannabis markets in various part...

Instead it argues it has led to a massive decrease in the criminal market, with the state now controlling 60% of sales.

The predicted tax take for 2015 is $125m (£81m) – of which $40m is to be allocated to school building programmes.

But home secretary Theresa May has repeatedly ruled out any relaxation of UK’s cannabis laws.

The Home Office maintains the long-term downward trend in drug misuse is evidence that the official drugs strategy is working.

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